1. Field of the Invention:
The present invention relates to a color copying apparatus in which a color copy image is obtained by exposing a plurality of photosensitive members with color decomposed images of an original color image to form electrostatic latent images of the color decomposed images thereon, respectively, developing these latent images with respective color developers to form visible images and transferring these visible images on a single transfer paper in an overlapping relation.
2. Discussion of Background:
FIG. 9 shows schematically a color copying apparatus. In this apparatus, a plurality of exposiong units 52a, 52b and 52c are arranged along a moving path of an original 51 and a corresponding number of photosensitive members 53a, 53b and 53c are exposed successively thereby with color decomposed images of the original to form color decomposed electrostatic latent images thereon while the original 51 moves along its path. The latent images are developed by different color developers by developing units 54a, 54b and 54c, respectively, and resultant visible color images are transferred onto a transfer paper 55 carried in an opposite direction, overlappingly. Then the overlapped images are fixed, resulting in a color copy.
In such color copying apparatus, the visible images on the photosensitive members 53a, 53b and 53c must be transferred onto the transfer paper 55 exactly without any relative deviation. Therefore, a moving speed of the original 51, a peripheral speed of each of the photosensitive members 53a to 53c and a moving speed of the transfer paper 55 must be maintained exactly, respectively.
In order to maintain these speeds exactly, it is usual to make the moving speed of the original 51 equal to the moving speed of the transfer paper 55, to make rotational speeds of the photosensitive members 53a to 53c equal to each other as well as to minimize eccentricities of the photosensitive members with respect to respective rotary shafts 56a, 56b and 56c thereof.
If these matters are done ideally, there may no deviation of color decomposed images transferred onto the transfer paper. However, it may be impossible to do them practically and therefore, a degradation of color copy image quality is practically unavoidable.
In the apparatus in which the respective photosensitive members are exposed successively to form the latent images thereon while the original is moving, a mounting table on which the original is mounted is moved by a pulley and a wire wound thereon. Therefore, when the pulley is eccentric, the moving speed of the mounting table fluctuates in each revolution of the pulley althogh an average speed thereof can be maintained constant. As a result, there may be produced a small relative deviation of latent images formed on the respective photosensitive members. This is detrimental to a final color copy image transferred on to the transfer paper after the developments thereof.